1984 Ski-Doo Shop Manual, Page 294Get this manual
SECTION 04 ELECTRICAL SYSTEM SUB-SECTION 03 (SPARK PLUGS)
DISASSEMBLY
First unscrew the spark plug one turnClean the spark plug and cylinder head with pressurize airThen unscrew completely
choke on, or running on too rich mixture due to faulty carburetor adjustment or incorrect fuel andor fuel mixingThe plug face of fouled spark plug has either dry coating of soot or an oily, glossy coating given by an excess either of oil or of oil with sootSuch coatings form conductive connection between the center electrode and ground
HEAT RANGE
The proper operating temperature or heat range of the spark plug is determined by the spark plug's ability to dissipate the heat generated by combustion The longer the heat path between the electrode tip to the plug shell, the hotter the spark plug operating tem perature will beand inversely, the shorter the heat path, the colder the operating temperature will beA "cold" type plug has relatively short insulator nose and transfers heat very rapidly into the cylinder headSuch plug is used in heavy duty or continuous high speed operation to avoid overheatingThe "hot" type plug has longer insulator nose and transfers heat more slowly away from its firing endIt runs hotter and burns off combustion deposits which might tend to foul the plug during prolonged idle or low speed operation